This application claims the benefit of Korean Patent Application No. 2000-40117, filed on Jul. 13, 2000 in Korea, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to an array substrate for a liquid crystal display device.
2. Description of Related Art
In general, liquid crystal display (LCD) devices make use of optical anisotropy and polarization properties of liquid crystal molecules to control arrangement orientation. The arrangement direction of the liquid crystal molecules can be controlled by an applied electric field. Accordingly, when an electric field is applied to liquid crystal molecules, the arrangement of the liquid crystal molecules changes. Since refraction of incident light is determined by the arrangement of the liquid crystal molecules, display of image data can be controlled by changing the electric field applied to the liquid crystal molecules.
Of the different types of known LCDs, active matrix LCDs (AM-LCDs), which have thin film transistors and pixel electrodes arranged in a matrix form, are the subject of significant research and development because of their high resolution and superiority in displaying moving images.
LCD devices have wide application in office automation (OA) equipment and video units because of their light, thin, low power consumption characteristics. The typical liquid crystal display (LCD) panel has an upper substrate, a lower substrate and a liquid crystal layer interposed therebetween. The upper substrate, commonly referred to as a color filter substrate, usually includes a common electrode and color filters. The lower substrate, commonly referred to as an array substrate, includes switching elements, such as thin film transistors (TFTs), and pixel electrodes.
As previously described, LCD device operation is based on the principle that the alignment direction of the liquid crystal molecules is dependent upon an electric field applied between the common electrode and the pixel electrode. Moreover, because the liquid crystal molecules have a spontaneous polarization characteristic, the liquid crystal layer is considered an optical anisotropy material. As a result of this spontaneous polarization characteristic, the liquid crystal molecules possess dipole moments when a voltage is applied to the liquid crystal layer between the common electrode and pixel electrode. Thus, the alignment direction of the liquid crystal molecules is controlled by the application of an electric field to the liquid crystal layer. When the alignment direction of the liquid crystal molecules is properly adjusted, incident light is refracted along the alignment direction to display image data. The liquid crystal molecules function as an optical modulation element having variable optical characteristics that depend upon polarity of the applied voltage.
FIG. 1 shows a typical LCD device. The LCD device 11 includes an upper substrate 5 and a lower substrate 22 with a liquid crystal layer 14 interposed therebetween. The upper substrate 5 and the lower substrate 22 are commonly referred to as a color filter substrate and an array substrate, respectively.
In the upper substrate 5 and upon the surface opposing the lower substrate 22, a black matrix 6 and a color filter layer 7 are formed in the shape of an array matrix and includes a plurality of red (R), green (G), and blue (B) color filters so that each color filter is surrounded by corresponding portions of the black matrix 6. Additionally, a common electrode 18 is formed on the upper substrate 5 that covers the color filter layer 7 and the black matrix 6. In the lower substrate 22 and upon the surface opposing the upper substrate 5, a thin film transistor (TFT) xe2x80x9cTxe2x80x9d, is formed in the shape of an array matrix corresponding to the color filter layer 7. A plurality of crossing gate lines 13 and data lines 15 are positioned such that each TFT xe2x80x9cTxe2x80x9d is located near each crossover point of the gate lines 13 and the data lines 15.
Furthermore, a plurality of pixel electrodes 17 are formed on a pixel region xe2x80x9cPxe2x80x9d that is defined by the gate lines 13 and the data lines 15 of the lower substrate 22. The pixel electrode 17 includes a transparent conductive material having good transmissivity such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO), for example.
According to the LCD device 11 of FIG. 1, a scanning signal is applied to a gate electrode of the TFT xe2x80x9cTxe2x80x9d through the gate line 13, while a data signal is applied to a source electrode of the TFT xe2x80x9cTxe2x80x9d through the data line 15. As a result, the liquid crystal molecules of the liquid crystal layer 14 are aligned and arranged by operation of the TFT xe2x80x9cTxe2x80x9d, and incident light passing through the liquid crystal layer 14 is controlled to display an image.
FIG. 2 is a plan view showing several pixels of an array substrate fabricated using a four-mask fabrication process for use in a conventional liquid crystal display device. FIG. 3 is an enlarged plan view of a thin film transistor xe2x80x9cTxe2x80x9d of FIG. 2.
In FIGS. 2 and 3, an array substrate 22 includes a plurality of pixel regions xe2x80x9cPxe2x80x9d each having a corresponding thin film transistor (TFT) xe2x80x9cTxe2x80x9d, a pixel electrode 17 and a storage capacitor xe2x80x9cCxe2x80x9d. Gate lines 13 are arranged in a transverse direction and data lines 15 are arranged in a longitudinal direction such that each pair of the gate lines 13 and the data lines 15 define a pixel region xe2x80x9cPxe2x80x9d. Each TFT xe2x80x9cTxe2x80x9d includes a gate electrode 26, a source electrode 28 and an active layer 33. The gate electrode 26 of each TFT xe2x80x9cTxe2x80x9d extends from the gate line 13, while the source electrode 28 of each TFT xe2x80x9cTxe2x80x9d extends from the data line 15. Furthermore, gate pads 18 are respectively positioned at ends of each gate line 13, while data pads 19 are respectively arranged at one end of each data line 15.
In general, both data lines 15 and gate lines 13 are classified into even numbered data lines and odd numbered data lines. The gate pads 18 and the data pads 19 are also correspondingly classified into even numbered gate and data pads and odd numbered gate and data pads. Among the gate lines 13 and the data lines 15, the even numbered lines and the odd numbered lines are respectively connected to different shorting bars to prevent discharge of static electricity from occurring in the gate lines 13 and the data lines 15.
In other words, because transparent glass substrates are conventionally used for substrates of LCD devices, any static electricity generated during manufacturing processes will flow into array pattern portions of the array substrate. Accordingly, the TFT, the gate lines and the data lines are all susceptible to significant damage as a result of any discharge of the static electricity. To prevent any damage due to any static electrical discharge, shorting bars are connected with the gate lines and the data lines.
For conventional array substrates fabricated using four-mask processes, one gate shorting bar is usually located at one end of the gate lines 13 and another gate shorting bar is usually located at another end of the gate lines 13. Each gate-shorting bar is connected with either the corresponding even or odd numbered gate line via the even or odd numbered gate pads. However, both gate shorting bars can be located at one end of the gate lines 13 and respectively be connected with either the even or odd numbered gate lines via the even or odd numbered gate pads. Furthermore, in the array substrate fabricated using a four-mask process as shown in FIG. 2, data shorting bars 29 and 32, which are formed in the same plane as the gate lines 13, are arranged at one end of the data lines 15 and respectively connected with either the even or odd numbered data lines via the corresponding even or odd numbered data pads.
In FIG. 2, odd numbered data pads are connected with first data pad connectors 42 (xe2x80x9cfirst connectors 42xe2x80x9d hereinafter) through data pad contact holes 39 (xe2x80x9cfirst contact holes 39xe2x80x9d hereinafter), and the first connectors 42 are connected with a first data shorting bar 29 through first shorting bar contact holes 40 (xe2x80x9csecond contact holes 40xe2x80x9d hereinafter). Accordingly, the odd numbered data lines are electrically connected with the first data shorting bar 29 via the first connectors 42 and odd numbered data pads. Moreover, the even numbered data pads are connected with second data pad connectors 43 (xe2x80x9csecond connectors 43xe2x80x9d hereinafter) through the first contact holes 39, and the second connectors 43 are connected with a second data shorting bar 32 through second shorting bar contact holes 41 (xe2x80x9cthird contact holes 41xe2x80x9d hereinafter). Accordingly, the even numbered data lines are electrically connected with the second data shorting bar 32 via the second connectors 43 and even numbered data pads.
In FIG. 2, since the second connectors 43 cross the first data shorting bar 29 and contact the second data shorting bar 32 through the third contact holes 41, the second connectors 43 and the first data shorting bar 29 can be short-circuited at intersections xe2x80x9cAxe2x80x9d of the first data shorting bar 29 and the second connectors 43. As shown in FIG. 4A, a gate insulation layer 31 covers the first data shorting bar 29 and the second data shorting bar 32 in the array substrate that is fabricated using a four-mask fabrication process. Portions xe2x80x9cAxe2x80x9d of the gate insulation layer (see FIG. 4D), the second connectors 43 and the first data shorting bar 29 short-circuit and make electrical connection.
FIGS. 4A to 4D are cross-sectional views taken along line IVxe2x80x94IV of FIG. 2 and show conventional fabricating processes of an array substrate. FIGS. 5A to 5D are cross-sectional views taken along line Vxe2x80x94V of FIG. 3 and show fabricating processes of a TFT xe2x80x9cTxe2x80x9d of FIG. 2.
Thin film transistors (TFTs) can be divided into two generally different categories based upon the relative disposition of their gate electrodesxe2x80x94staggered types and coplanar types. The staggered type TFT includes an inverted staggered type which are generally used for LCD devices due to their simple structure and superior efficiency. Within the inverted staggered type TFT there includes a back channel etched type (EB) and an etch stopper type (ES). A manufacturing method of the back channel etched type TFT will be explained hereinafter.
Referring to FIGS. 4A and 5A, a substrate 22 is first cleaned of organic materials and alien substances to promote adhesion with a first metal layer that is subsequently deposited on the substrate 22 by a sputtering process. Then, the first metal layer is patterned using a first mask to form the gate lines 13 (see FIGS. 2 and 3) in a transverse direction, a gate electrode 26 that extends from each gate line, the gate pads 18 (see FIG. 2) that are disposed at opposite ends of the gate lines, first and second gate shorting bars (not shown) that are perpendicular to the gate lines and respectively contact odd numbered gate pads and even numbered gate pads, and first and second data shorting bars 29 and 32 that are formed parallel with the gate lines and spaced apart from each other.
Referring to FIGS. 4A and 5A, aluminum is conventionally used as a metal for the first metal layer because of its low resistance and reduced RC delay. However, pure aluminum is chemically weak when exposed to acidic processing and may result in formation of hillocks during high temperature processing. Accordingly, aluminum alloys and multi-layered aluminum structures are used for the first metal layer.
Still referring to FIGS. 4A and 5A, the gate insulation layer 31 is formed on an entire surface of the substrate 22 and covers the patterned first metal layer. Then, a pure amorphous silicon (a-Si:H) layer 33 (often referred to as an active layer) and a doped amorphous silicon (n+a-Si:H) layer 35 (often referred to as an ohmic contact layer) are formed in series upon the gate insulation layer 31. Moreover, a second metal layer 28 is formed upon the doped amorphous silicon (n+a-Si:H) layer 35 by depositing molybdenum (Mo). The doped amorphous silicon (n+a-Si:H) layer 35 reduces the contact resistance between the pure amorphous silicon (a-Si:H) layer 33 and the second metal layer 28.
Now, referring to FIGS. 4B and 5B, the second metal layer 28 is patterned using a second mask to form a first hole 45 disposed over the gate electrode 26. By forming the first hole 45, the patterned second metal 28 disposed over the gate electrode 26 is divided into two regions that will become source electrode 30 and drain electrode 31 (in FIG. 5C) in a later step. The two portions of the patterned second metal 28 arranged at left and right sides of the first hole 45, as shown in FIG. 5B, overlap opposite ends of the gate electrode 26. Moreover, when forming the first hole 45, a second hole (not shown) is formed over the first data shorting bar 29 and a third hole 46 is formed over the second data shorting bar 32 by patterning portions of the second metal layer 28. The second hole (not show) and the third hole 46 in the second metal layer 28 respectively become a second contact hole 40 (in FIG. 2) and a third contact hole 41 (in FIG. 4C) in a later step.
Thereafter, a portion of the ohmic contact layer 35 disposed upon the active layer 33 is etched using the patterned second metal layer 28 as a mask, thereby forming a channel region xe2x80x9cCHxe2x80x9d below the first hole 45 in the active layer 33. Subsequently, a passivation layer 37 is formed over the remaining portions of the patterned second metal layer 28.
Now, referring to FIGS. 4C and 5C, the passivation layer 37, the second metal layer 28, the ohmic contact layer 35 and the active layer 33 are simultaneously patterned using a third mask to form the data line 15, the data pad 19, the source electrode 30 and the drain electrode 31. Accordingly, each pair of gate lines and data lines define a pixel region xe2x80x9cPxe2x80x9d (in FIG. 2), and the gate insulation layer 31 remains in the pixel region. Furthermore, in the third mask process, a first contact hole 39 is formed extending through the data pad 19. Additionally, a second contact hole 40 (in FIG. 2) disposed over the first data shorting bar 29 and a third contact hole 41 disposed over the second data shorting bar 32 are formed respectively due to formation of the second hole (not show) and a third hole 46 (in FIG. 4B).
Referring to FIG. 5C, a side portion of the drain electrode 31 is exposed during the above-mentioned patterning process. Further, although not depicted in the drawings, gate pad contact holes are formed disposed over the gate pads 18 (in FIG. 2) by patterning stacked layers over the gate pads.
In the above-mentioned patterning process, a dry etching process method is used. After the third mask process, the source electrode 30, the drain electrode 31, the data line 15, and the data pad 19 are formed into desired shapes. However, during this patterning process, defects including pinholes and/or cracks can be created in the gate insulation layer. When these defects are created over the first data shorting bar 29, an electrical short can occur between the first data shorting bar 29 and a subsequently formed connector.
Now, referring to FIGS. 4D and 5D, a transparent conductive material is deposited and patterned to form pixel electrode 17, first connector 42 (in FIG. 2) and second connector 43. Accordingly, the pixel electrode 17 contacts the exposed side portion of the drain electrode 31 and is positioned in the pixel region xe2x80x9cPxe2x80x9d (in FIG. 2). Moreover, the second connector 43 that crosses the first data shorting bar 29 connects the data pad 19 to the second data shorting bar 32 via the first contact hole 39 and the third contacts hole 41. As a result, the even numbered data line 15 is electrically connected with the second data shorting bar 32. Further, as shown in FIG. 2, the first connector 42 electrically connects the odd numbered data lines to the first data shorting bar 29 via the first contact hole 39 and the second contact hole 40.
In the aforementioned structure, when the defects xe2x80x9cDxe2x80x9d such as pin holes and/or cracks exists in a portion xe2x80x9cAxe2x80x9d over the first data shorting bar 29, the first data shorting bar 29 and the second connector 43 are electrically short-circuited in the portion xe2x80x9cAxe2x80x9d. This electrical short prevents accurate results in short/open-circuit testing using the shorting bars. As a result, manufacturing defects can occur in the array substrate, thereby decreasing manufacturing yields of the LCD device.
Accordingly, the present invention is directed to an array substrate for a liquid crystal display and method for fabricating thereof that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an array substrate for a liquid crystal display device having improved resistance to electrical short-circuiting.
Another object of the present invention is to provide a method of fabricating an array substrate for a liquid crystal display device with decreased defects to increase manufacturing yields.
Additional features and advantages of the invention will be set forth in the description that follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an array substrate for a liquid crystal display device includes a substrate, a plurality of thin film transistors formed on the substrate, each thin film transistor comprises a gate electrode, a source electrode and a drain electrode, a plurality of gate lines arranged in one direction on the substrate, each gate line connected with the gate electrodes of the plurality of thin film transistors and each gate line has a gate pad disposed at a first end thereof, a plurality of data lines arranged perpendicular to the plurality of gate lines on the substrate, each data line connected to the source electrodes of the plurality of thin film transistors and each data line has a data pad disposed at a first end thereof, a plurality of pixel electrodes located at pixel regions defined by intersections of the plurality of gate lines and the plurality of data lines, each pixel electrode contacting each drain electrode of the plurality of thin film transistors, a first data shorting bar arranged parallel with the plurality of gate lines at the first end of the data lines, a second data shorting bar arranged parallel with the plurality of gate lines at the first end of the gate lines and spaced apart from the first data shorting bar, a plurality of first connectors electrically connecting the odd numbered data lines to the first data shorting bar, a plurality of second connectors electrically connecting the even numbered data lines to the second data shorting bar, and a plurality of patterned insulating segments formed over the first shorting bar and below the plurality of second connectors, wherein each patterned insulating segment is disposed at an intersection between the first data shorting bar and each second connector.
In another aspect, a method of fabricating a liquid crystal display device includes the steps of forming a first metal layer on a substrate, patterning the first metal layer to form a gate line, a gate electrode, a gate pad, a first shorting bar, and a second shorting bar, forming a gate insulation layer, a pure amorphous silicon layer, a doped amorphous silicon layer and a second metal layer to cover the patterned first metal layer, patterning the second metal layer and the doped amorphous silicon layer to form first, second and third through-holes and first and second grooves to expose a portion of the pure amorphous silicon layer, the first and second grooves creating an isolated portions of the second metal layer, forming a passivation layer to cover the patterned second metal layer, forming a source electrode, a drain electrode, a data line, a data pad, an insulating segment, and first, second and third contact holes, and forming a pixel electrode, a first connector and a second connector of a transparent conductive material.
In another aspect, an array substrate having thin film transistors, pixel electrodes, gate lines and data lines, wherein each thin film transistor is formed at a crossover point of each pairs of gate lines and data lines, and wherein each pixel electrode is formed in a pixel region defined by each of the pairs of gate lines and data lines, includes a plurality of data pads formed at a first end of the data lines and connected thereto, the data pads including odd numbered data pads and even numbered data pads, each data pad having a first contact hole, a first shorting bar formed adjacent to the data pads and arranged perpendicular to the data lines, a second shorting bar spaced apart from and arranged parallel with the first shorting bar, a gate insulation layer covering the gate lines, the first shorting bar, and the second shorting bar, the gate insulation layer having second and third contact holes, wherein the second contact holes are formed over the first shoring bar, and wherein the third contact holes are formed over the second shorting bar, a first connector connecting the odd numbered data pads to the first shorting bar through the first and second contact holes, a plurality of second connectors each crossing the first shorting bar and connecting the even numbered data pads to the second shorting bar through the first and third contact holes, and a plurality of island-shaped insulating segments formed between the first shorting bar and each second connector at each intersection of the first shorting bar and the second connector, each insulating segment electrically insulating the first shorting bar from each second connector.
In another aspect, a liquid crystal display device includes a substrate, a plurality of gate lines on the substrate, a plurality of data lines on the substrate and disposed perpendicular to the plurality of gate lines, a first data shorting bar arranged parallel with the plurality of gate lines at a first end of the data lines, a second data shorting bar arranged parallel with the plurality of gate lines at a first end of the gate lines and spaced apart from the first data shorting bar, a plurality of first connectors electrically connecting odd numbered data lines to the first data-shorting bar, a plurality of second connectors electrically connecting even numbered data lines to the second data shorting bar, and a plurality of patterned insulating segments formed over the first shorting bar and below the plurality of second connectors, wherein each patterned insulating segment is disposed at an intersection between the first data shorting bar and each second connector.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.